The above research project is concerned with the purification and characterization of each of the enzymes involved in the stepwise reduction of nitrate to ammonia (i.e., nitrate assimilation) and in nitrate respiration (where nitrate replaces molecular oxygen as the terminal electron acceptor) including dinitrification. It includes the investigation of the possibility that nitrate assimilation proceeds via organic intermediates rather than inorganic ones; and will also examine the adaptive formation and metabolic control of the enzymes concerned with nitrate assimilation and nitrate respiration. Particular emphasis will be placed on the characterization and mechanism of action of the now highly purified and crystalline assimilatory nitrate reductase enzyme from Neurospora. It will include not only a detailed examination of each of the steps catalyzed by the enzyme, but investigations of several mutant forms of the enzyme, the properties of the induction of nitrate reductase, and several other aspects of its synthesis. The experimental material for these investigations are Neurospora (wild type, and several particular mutants), bacteria and tissues of higher plants. Aside from their academic biological value, the data could prove to be useful in interpreting and evaluating the relationship between nutritive value and yield with respect to the use of different nitrogen compounds in agricultural practice.